Intact Cerebellum Research Articles

Synaptic mechanisms for associative learning in the cerebellar nuclei

Associative learning during delay eyeblink conditioning (EBC) depends on an intact cerebellum. However, the relative contribution of changes in the cerebellar nuclei to learning remains a subject of ongoing debate. In particular, little is known about the changes in synaptic inputs to cerebellar nuclei neurons that take place during EBC and how they shape the membrane potential of these neurons. Here, we probed the ability of these inputs to support associative learning in mice, and investigated structural and cell-physiological changes within the cerebellar nuclei during learning. We find that optogenetic stimulation of mossy fiber afferents to the anterior interposed nucleus (AIP) can substitute for a conditioned stimulus and is sufficient to elicit conditioned responses (CRs) that are adaptively well-timed. Further, EBC induces structural changes in mossy fiber and inhibitory inputs, but not in climbing fiber inputs, and it leads to changes in subthreshold processing of AIP neurons that correlate with conditioned eyelid movements. The changes in synaptic and spiking activity that precede the CRs allow for a decoder to distinguish trials with a CR. Our data reveal how structural and physiological modifications of synaptic inputs to cerebellar nuclei neurons can facilitate learning.

Synaptic Mechanisms of Delay Eyeblink Classical Conditioning: AMPAR Trafficking and Gene Regulation in an In Vitro Model.

An in vitro model of delay eyeblink classical conditioning was developed to investigate synaptic plasticity mechanisms underlying acquisition of associative learning. This was achieved by replacing real stimuli, such as an airpuff and tone, with patterned stimulation of the cranial nerves using an isolated brainstem preparation from turtle. Here, our primary findings regarding cellular and molecular mechanisms for learning acquisition using this unique approach are reviewed. The neural correlate of the in vitro eyeblink response is a replica of the actual behavior, and features of conditioned responses (CRs) resemble those observed in behavioral studies. Importantly, it was shown that acquisition of CRs did not require the intact cerebellum, but the appropriate timing did. Studies of synaptic mechanisms indicate that conditioning involves two stages of AMPA receptor (AMPAR) trafficking. Initially, GluA1-containing AMPARs are targeted to synapses followed later by replacement by GluA4 subunits that support CR expression. This two-stage process is regulated by specific signal transduction cascades involving PKA and PKC and is guided by distinct protein chaperones. The expression of the brain-derived neurotrophic factor (BDNF) protein is central to AMPAR trafficking and conditioning. BDNF gene expression is regulated by coordinated epigenetic mechanisms involving DNA methylation/demethylation and chromatin modifications that control access of promoters to transcription factors. Finally, a hypothesis is proposed that learning genes like BDNF are poised by dual chromatin features that allow rapid activation or repression in response to environmental stimuli. These in vitro studies have advanced our understanding of the cellular and molecular mechanisms that underlie associative learning.

Feasibility of Cerebellar Transcranial Direct Current Stimulation to Facilitate Goal-Directed Weight Shifting in Chronic Post-Stroke Hemiplegics.

Neurological disorder such as stroke can adversely affect one's weight-bearing symmetry leading to dysfunctional postural control. Recovery after stroke is facilitated through functionally-relevant neuroplastic modulation. Functionally-relevant cerebellum coordinates voluntary movements. Specifically, the dentate nuclei and lower limb representations (lobules VII-IX) of the cerebellum are involved in error-correction, crucial for postural control. It is postulated that cerebellar transcranial direct current stimulation (ctDCS) of the dentate nuclei and lobules VII-IX can modulate postural control in chronic stroke survivors. The objectives of this work were to (1) present a refined Virtual Reality (VR)-based balance training platform (VBaT) that can measure Center of Pressure (CoP) and (2) carry out a study to understand the implication of ctDCS stimulating the dentate nuclei (PhaseD) and lobules VII-IX (PhaseL) on the postural control of chronic stroke patients when they interacted with VBaT. Also, we investigated whether hemiplegic patients (with intact cerebellum) having Basal Ganglia (BG) infarction had any differential abilities to correct postural sway from those with no BG infarction (while shifting weight to the Affected side). Results of a single-session single-blind crossover study on randomized PhaseD and PhaseL stimulation (with an intermediate resting state bipolar bilateral ctDCS) on 12 chronic hemiplegic patients on separate days indicated differentiated findings (post stimulation) on CoP-related indices. We observed an incremental effect on one's postural control during PhaseD and inhibitory effect on the dentate nuclei during PhaseL. Clustering analysis showed that those with BG infarction demonstrated poor postural control and deficit in error correction ability irrespective of the ctDCS Phase.

A Fast Optical Method to Direct High Linage-Commitment Stem-Cell Differentiation by a Short Flash of Ultrafast Laser Activation <i>In vitro</i> and <i>In vivo</i>

Recent technological advancements on stem-cell differentiation induction have been making great progresses in stem-cell research, regenerative medicine and therapeutic applications by developments of gene editing, biomaterials, physical stimulations, and specially-designed materials. In this report, we present a noninvasive all-optical strategy to induce stem-cell differentiation in vitro and in vivo in which a microscopic scheme with a femtosecond laser is developed to activate target stem cells in situ in a controllable and spatiotemporal-specific manner. A 100-ms transient laser irradiation to a submicron cytoplasmic region inside cells induces adipose-derived stem cells to differentiate to osteoblasts with high linage-commitment that cannot further transdifferentiate. The fast laser activation directly initiates differentiation of mouse cerebellar granule neuron progenitors to granule neurons through the skull in the intact cerebellum of mice. This noninvasive technology works on cells and animals without any genetic manipulations or exogenous biomaterials, hence holding promising potential in biomedical researches and cell-based therapies.

Dysfunction of cerebellum functional connectivity between default mode network and cerebellar structures in patients with mild traumatic brain injury in acute stage. rsfMRI study

Mild traumatic brain injury (mTBI) is the most common neurological damage in children that's why it is extremely important to identify and analyze biomarkers that can help in predicting patient's treatment and recovery in period of mTBI. Aim of this study is to verify a hypothesis that functional connectivity disturbances between intact cerebellum and DMN nodes are included in symptomatic manifestation of mTBI.Methods. 28 MR negative patients with mTBI were studied in age from 12 to 17 years (mean age – 14.7 years). The control group consisted of 23 healthy children. All MRI studies wereperformed on a Philips AchievadStream 3.0 T scanner equipped with a 32-channelPhilips dStream head coil. A 4 min rsfMRI gradient-echo echo planar imaging (EPI)sequence was acquired (TR = 3000 ms, echo time (TE) = 30 ms, 80 dynamics withdynamic scan time = 3 s). fMRI data were processed using functional connectivitytoolbox CONN.Results. No statistically significant differences in correlation strengths between control group and group of patients were detected as a result of DMN analysis. Intergroup seed-basedcorrelation ROI analysis revealed statistically significant (p < 0.05) differencein links between DMN regions and vermis (cerebellum): positive link in control group and negative link in groupof patients.Conclusions. The revealed changes in DMN neuronal connection and cerebellar regions in acute stage of mTBI patients can be an initial step of damages leading to cognitive deficit which can be developed in future.

Glissades Are Altered by Lesions to the Oculomotor Vermis but Not by Saccadic Adaptation.

Saccadic eye movements enable fast and precise scanning of the visual field, which is partially controlled by the posterior cerebellar vermis. Textbook saccades have a straight trajectory and a unimodal velocity profile, and hence have well-defined epochs of start and end. However, in practice only a fraction of saccades matches this description. One way in which a saccade can deviate from its trajectory is the presence of an overshoot or undershoot at the end of a saccadic eye movement just before fixation. This additional movement, known as a glissade, is regarded as a motor command error and was characterized decades ago but was almost never studied. Using rhesus macaques, we investigated the properties of glissades and changes to glissade kinematics following cerebellar lesions. Additionally, in monkeys with an intact cerebellum, we investigated whether the glissade amplitude can be modulated using multiple adaptation paradigms. Our results show that saccade kinematics are altered by the presence of a glissade, and that glissades do not appear to have any adaptive function as they do not bring the eye closer to the target. Quantification of these results establishes a detailed description of glissades. Further, we show that lesions to the posterior cerebellum have a deleterious effect on both saccade and glissade properties, which recovers over time. Finally, the saccadic adaptation experiments reveal that glissades cannot be modulated by this training paradigm. Together our work offers a functional study of glissades and provides new insight into the cerebellar involvement in this type of motor error.

Brain Stem and Audio-Vestibular Regulation.

The central pathologies present with perverted auditory perception and compromised postural control. Considering the existing controversy this study involves assessments of 100 cases of post fossa tumefactions in which a detailed clinical and neuro-otological (pure tone audiometry, electronystagmography, brainstem evoked response audiometry) profile is compared with their imaging patterns. The CP angle schwannomas (N = 26) presented with abnormal speech tests (N = 18), abnormal auditory adaptation (N = 7) and ABR with pathologically increased latency of wave V (N = 32), poor formation of wave I (N = 31) along with abnormal inter-wave interval (N = 32). In lesions (N = 32) compressing deeper nuclei, vermis and axial parts of brain stem, a gross truncal ataxia, incoordination, nystagmus, speech defects, subtotal deafness and bilateral ABR abnormalities were observed. The abnormal optomotor activities were seen as saccadic (N = 44) and deformed slow pursuit eye movements (N = 20). Inability to sustain holding function resulted in gaze nystagmus (N = 71), and poor timing manifested as fixation overshoots (N = 42). The midline cerebellar and upper brain stem lesions revealed bilateral OKN abnormalities whereas paramedian pathology showed only ipsilateral distortion. Caloric tests revealed culmination frequency as the most sensitive parameter for assessment of the hypo-reflexia in diffuse cerebellopathies while slow phase velocity in cases of posterior fossa lesion. The caloric hypo-activity appears to be of a better localizing value than the directional preponderance. The slow pursuit tracking revealed Type III curve perhaps due to defective regulation of slow movements in partially intact cerebellum (N = 15), while gross cerebellar dysfunctioning resulted into Type IV curve (N = 5).

Cerebellar Control of Ocular Movements: Application to the Topographical Diagnosis of Cerebellar Lesions

Over the last decade, substantial information on cerebellar oculomotor control has been provided by the use of sophisticated neuroanatomical, neurophysiological, and imaging techniques. We now know that an intact cerebellum is a prerequisite for normal oculomotor performance. This review clarifies the current knowledge on structure-function correlations of the cerebellum in relation to ocular movements and allows them to be applied to topographical diagnosis of cerebellar lesions. The cerebellar regions most closely related to oculomotor function are: (1) the flocculus/paraflocculus for VOR suppression, cancellation, smooth pursuit eye movement and gaze-holding, (2) the nodulus/ventral uvula for velocity storage and low frequency prolonged vestibular response, and (3) the dorsal oculomotor vermis (declive VI, folium VII) and the posterior portion of the fastigial nucleus (fastigial oculomotor region) for saccades and smooth pursuit initiation. Symptomatically, defects in the flocculus/parflocculus cause saccadic pursuit, downbeat nystagmus, and impairments to visual suppression of the VOR. Lesions of the nodulus/uvula reveal as periodic alternating nystagmus. Lesions of the oculomotor vermis and the fastigial nucleus can induce saccadic dysmetria, while fastigial nucleus lesions may also cause ocular flutter/opsoclonus. A detailed knowledge of cerebellar anatomy and the physiology of eye movements enables localization of lesions to specific areas of the cerebellum.

Direct neural current imaging in an intact cerebellum with magnetic resonance imaging

The ability to detect neuronal currents with high spatiotemporal resolution using magnetic resonance imaging (MRI) is important for studying human brain function in both health and disease. While significant progress has been made, we still lack evidence showing that it is possible to measure an MR signal time-locked to neuronal currents with a temporal waveform matching concurrently recorded local field potentials (LFPs). Also lacking is evidence that such MR data can be used to image current distribution in active tissue. Since these two results are lacking even in vitro, we obtained these data in an intact isolated whole cerebellum of turtle during slow neuronal activity mediated by metabotropic glutamate receptors using a gradient-echo EPI sequence (TR=100ms) at 4.7T. Our results show that it is possible (1) to reliably detect an MR phase shift time course matching that of the concurrently measured LFP evoked by stimulation of a cerebellar peduncle, (2) to detect the signal in single voxels of 0.1mm3, (3) to determine the spatial phase map matching the magnetic field distribution predicted by the LFP map, (4) to estimate the distribution of neuronal current in the active tissue from a group-average phase map, and (5) to provide a quantitatively accurate theoretical account of the measured phase shifts. The peak values of the detected MR phase shifts were 0.27–0.37°, corresponding to local magnetic field changes of 0.67–0.93nT (for TE=26ms). Our work provides an empirical basis for future extensions to in vivo imaging of neuronal currents.

Fast calcium sensor proteins for monitoring neural activity.

A major goal of the BRAIN Initiative is the development of technologies to monitor neuronal network activity during active information processing. Toward this goal, genetically encoded calcium indicator proteins have become widely used for reporting activity in preparations ranging from invertebrates to awake mammals. However, slow response times, the narrow sensitivity range of Ca2+ and in some cases, poor signal-to-noise ratio still limit their usefulness. Here, we review recent improvements in the field of neural activity-sensitive probe design with a focus on the GCaMP family of calcium indicator proteins. In this context, we present our newly developed Fast-GCaMPs, which have up to 4-fold accelerated off-responses compared with the next-fastest GCaMP, GCaMP6f. Fast-GCaMPs were designed by destabilizing the association of the hydrophobic pocket of calcium-bound calmodulin with the RS20 binding domain, an intramolecular interaction that protects the green fluorescent protein chromophore. Fast-GCaMP6f-RS06 and Fast-GCaMP6f-RS09 have rapid off-responses in stopped-flow fluorimetry, in neocortical brain slices, and in the intact cerebellum in vivo. Fast-GCaMP6f variants should be useful for tracking action potentials closely spaced in time, and for following neural activity in fast-changing compartments, such as axons and dendrites. Finally, we discuss strategies that may allow tracking of a wider range of neuronal firing rates and improve spike detection.

The cerebellum and visual perceptual learning: Evidence from a motion extrapolation task

Visual perceptual learning is widely assumed to reflect plastic changes occurring along the cerebro-cortical visual pathways, including at the earliest stages of processing, though increasing evidence indicates that higher-level brain areas are also involved. Here we addressed the possibility that the cerebellum plays an important role in visual perceptual learning. Within the realm of motor control, the cerebellum supports learning of new skills and recalibration of motor commands when movement execution is consistently perturbed (adaptation). Growing evidence indicates that the cerebellum is also involved in cognition and mediates forms of cognitive learning. Therefore, the obvious question arises whether the cerebellum might play a similar role in learning and adaptation within the perceptual domain. We explored a possible deficit in visual perceptual learning (and adaptation) in patients with cerebellar damage using variants of a novel motion extrapolation, psychophysical paradigm. Compared to their age- and gender-matched controls, patients with focal damage to the posterior (but not the anterior) cerebellum showed strongly diminished learning, in terms of both rate and amount of improvement over time. Consistent with a double-dissociation pattern, patients with focal damage to the anterior cerebellum instead showed more severe clinical motor deficits, indicative of a distinct role of the anterior cerebellum in the motor domain. The collected evidence demonstrates that a pure form of slow-incremental visual perceptual learning is crucially dependent on the intact cerebellum, bearing the notion that the human cerebellum acts as a learning device for motor, cognitive and perceptual functions. We interpret the deficit in terms of an inability to fine-tune predictive models of the incoming flow of visual perceptual input over time. Moreover, our results suggest a strong dissociation between the role of different portions of the cerebellum in motor versus non-motor functions, with only the posterior lobe being responsible for learning in the perceptual domain.

Predicting and correcting ataxia using a model of cerebellar function.

Cerebellar damage results in uncoordinated, variable and dysmetric movements known as ataxia. Here we show that we can reliably model single-joint reaching trajectories of patients (n = 10), reproduce patient-like deficits in the behaviour of controls (n = 11), and apply patient-specific compensations that improve reaching accuracy (P < 0.02). Our approach was motivated by the theory that the cerebellum is essential for updating and/or storing an internal dynamic model that relates motor commands to changes in body state (e.g. arm position and velocity). We hypothesized that cerebellar damage causes a mismatch between the brain's modelled dynamics and the actual body dynamics, resulting in ataxia. We used both behavioural and computational approaches to demonstrate that specific cerebellar patient deficits result from biased internal models. Our results strongly support the idea that an intact cerebellum is critical for maintaining accurate internal models of dynamics. Importantly, we demonstrate how subject-specific compensation can improve movement in cerebellar patients, who are notoriously unresponsive to treatment.

Altered Accuracy of Saccadic Eye Movements in Children with Fetal Alcohol Spectrum Disorder

Prenatal exposure to alcohol is a major, preventable cause of neurobehavioral dysfunction in children worldwide. The measurement and quantification of saccadic eye movements is a powerful tool for assessing sensory, motor, and cognitive function. The quality of the motor process of an eye movement is known as saccade metrics. Saccade accuracy is 1 component of metrics, which to function optimally requires several cortical brain structures as well as an intact cerebellum and brain-stem. The cerebellum has frequently been reported to be damaged by prenatal alcohol exposure. This study, therefore, tested the hypothesis that children with fetal alcohol spectrum disorder (FASD) will exhibit deficits in the accuracy of saccades. A group of children with FASD (n = 27) between the ages of 8 and 16 and typically developing control children (n = 27) matched for age and sex, completed 3 saccadic eye movement tasks of increasing difficulty. Eye movement performance during the tasks was captured using an infrared eye tracker. Saccade metrics (e.g., velocity, amplitude, accuracy) were quantified and compared between the 2 groups for the 3 different tasks. Children with FASD were more variable in saccade endpoint accuracy, which was reflected by statistically significant increases in the error of the initial saccade endpoint and the frequency of additional, corrective saccades required to achieve final fixation. This increased variability in accuracy was amplified when the cognitive demand of the tasks increased. Children with FASD also displayed a statistically significant increase in response inhibition errors. These data suggest that children with FASD may have deficits in eye movement control and sensory-motor integration including cerebellar circuits, thereby impairing saccade accuracy.

Neuroimaging of Dandy-Walker Malformation

Dandy-Walker malformation (DWM) is the most common human cerebellar malformation, characterized by hypoplasia of the cerebellar vermis, cystic dilation of the fourth ventricle, and an enlarged posterior fossa with upward displacement of the lateral sinuses, tentorium, and torcular. Although its pathogenesis is not completely understood, there are several genetic loci related to DWM as well as syndromic malformations and congenital infections. Dandy-Walker malformation is associated with other central nervous system abnormalities, including dysgenesis of corpus callosum, ectopic brain tissue, holoprosencephaly, and neural tube defects. Hydrocephalus plays an important role in the development of symptoms and neurological outcome in patients with DWM, and the aim of surgical treatment is usually the control of hydrocephalus and the posterior fossa cyst. Imaging modalities, especially magnetic resonance imaging, are crucial for the diagnosis of DWM and distinguishing this disorder from other cystic posterior fossa lesions. Persistent Blake's cyst is seen as a retrocerebellar fluid collection with cerebrospinal fluid signal intensity and a median line communication with the fourth ventricle, commonly associated with hydrocephalus. Mega cisterna magna presents as an extraaxial fluid collection posteroinferior to an intact cerebellum. Retrocerebellar arachnoid cysts frequently compress the cerebellar hemispheres and the fourth ventricle. Patients with DWM show an enlarged posterior fossa filled with a cystic structure that communicates freely with the fourth ventricle and hypoplastic vermis. Comprehension of hindbrain embryology is of utmost importance for understanding the cerebellar malformations, including DWM, and other related entities.

Influence of cerebellar malformations on cerebral volume: does it matter?

The cerebellum is not only important for motor functions, but also affects a wide range of cognitive tasks including executive functions, spatial perception, language and speech, and affective functions. This was highlighted by Schmahmann and Sherman1 in their description and conceptualization of the cerebellar cognitive affective syndrome (CCAS). Since then, the impact of the cerebellum on cognitive functions has been increasingly shown in cerebellar malformations.2 Even though the pattern of cognitive impairment in cerebellar malformations is less specific than in acquired focal cerebellar lesions, it is still reminiscent of the CCAS. The anatomical basis of the cerebellar role in higher cognitive functions is the existence of cerebro-cerebellar connections (cortico-ponto-cerebellar and cerebello-thalamo-cortical loops) that link the cerebellum with associative regions in the prefrontal, posterior parietal, superior temporal polymodal regions, and dorsal parastriate cortices as well as with the limbic/paralimbic regions. The interaction between cerebellum and cerebrum may affect the anatomical structures involved in terms of volume. In preterm infants, unilateral cerebral parenchymal brain injuries have been shown to result in subsequent impairment in the contralateral cerebellar volume and, conversely, primary unilateral cerebellar injuries were reported to be associated with impaired contralateral cerebral brain volume at term.3 Bolduc et al.4 demonstrate that cerebellar volumetric impairment is associated with altered growth in specific cerebral regions and attribute this to cerebellar malformations.5 Although the small number of children included and the heterogeneous cohort of patients may be limitations of the study (in terms of different cerebellar malformations), the authors demonstrated significantly reduced volume in the deep grey matter nuclei, inferior occipital grey matter, and subgenual and midtemporal white matter. The developing cerebrum, therefore, appears to require an intact cerebellum to achieve its normal structure and volume as the result of a trophic transynaptic effect. The authors hypothesize that the associated regional reductions in cerebral volumes may represent a possible mechanism underlying developmental disabilities and cognitive impairment in children with cerebellar malformations. The interaction between cerebellum and cerebrum, however, is not limited only to a trophic transsynaptic effect, but may also lead to a cerebral cortical functional impairment. The posterior fossa syndrome is a particularly acute form of the CCAS characterized by cerebellar dysfunction, oromotor apraxia, emotional lability, and mutism in patients after infratentorial injury. This syndrome is a good example of functionally disrupted cerebro-cerebellar connections.6 In children with the posterior fossa syndrome, low fractional anisotropy values in the bilateral superior cerebellar peduncles, bilateral fornices, white matter region proximate to the right angular gyrus, and white matter region proximate to the left superior frontal gyrus have been found.6 These results show that proximal lesions of the dentato-thalamo-cortical pathway may lead to a functional disconnection between the cerebellum and the associate cortical regions and, subsequently, cause the characteristic neurocognitive impairment in the posterior fossa syndrome. I am not aware of any study in the literature showing cerebro-cerebellar functional disconnection in cerebellar malformations. It is plausible that in cerebellar malformations, both regional reductions in cerebral volumes due to a transynaptic trophic effect as well as functional disconnection in the cerebro-cerebellar white matter pathway may play a pathogenetic role causing cognitive problems. The combination of volumetric and connectivity studies may further increase our understanding of the role of the cerebellum in cognitive functions.

Cerebellum and Ocular Motor Control

An intact cerebellum is a prerequisite for optimal ocular motor performance. The cerebellum fine-tunes each of the subtypes of eye movements so they work together to bring and maintain images of objects of interest on the fovea. Here we review the major aspects of the contribution of the cerebellum to ocular motor control. The approach will be based on structural–functional correlation, combining the effects of lesions and the results from physiologic studies, with the emphasis on the cerebellar regions known to be most closely related to ocular motor function: (1) the flocculus/paraflocculus for high-frequency (brief) vestibular responses, sustained pursuit eye movements, and gaze holding, (2) the nodulus/ventral uvula for low-frequency (sustained) vestibular responses, and (3) the dorsal oculomotor vermis and its target in the posterior portion of the fastigial nucleus (the fastigial oculomotor region) for saccades and pursuit initiation.

Comparison of P19-Derived Neuroprogenitor and Naive Cell Survival after Intracerebellar Application into B6CBA Mice

Mouse embryonic carcinoma cells (P19 line) were studied for both their survival and developmental potential in the intact cerebellum of B6CBA mice. The P19 cells were cultured and labelled with green fluorescent protein using transfection. Cells were used for transplantation either in the undifferentiated stage or after 3 days of neurodifferentiation induced by retinoic acid. The intracerebellar application was performed in 43 mice: group A (N = 21) received neuroprogenitors and group B (N = 22) received undifferentiated cells. The morphology of transplanted cells within the context of the surrounding cerebellar tissue was evaluated after 3 weeks. Naive P19 cells engrafted and survived in the cerebellum of 7 of the 22 adult mice (survival rate 31.8 %). Neuroprogenitors survived in 13 of the 21 mice (survival rate was 61.9 %). Since the cut-off is P &lt; 0.05, the difference is not statistically significant (P = 0.069). An expansive appearance of the graft was significantly more frequent (P = 0.0047) in naive P19 cells than in neuroprogenitors. In mice in which the grafts did not survive, no marks of grafted cells or only fluorescing detritus were found. In conclusion, this is the first study to track the fate and morphology of embryonic carcinoma cells transplanted into the cerebellum, confirming that neuroprogenitors derived from embryonic carcinoma cells can settle in the host tissue and differentiate according to the surrounding conditions. With further validation, the embryonic carcinoma cells could become a valuable model with which to study the impact of cell therapy on neurodegenerative diseases.

Origin and timing of voltage-sensitive dye signals within layers of the turtle cerebellar cortex

Optical recording techniques were applied to the turtle cerebellum to localize synchronous responses to microstimulation of its cortical layers and reveal the cerebellum's three-dimensional processing. The in vitro yet intact cerebellum was first immersed in voltage-sensitive dye and its responses while intact were compared to those measured in thick cerebellar slices. Each slice is stained throughout its depth, even though the pial half appeared darker during epi-illumination and lighter during trans-illumination. Optical responses were shown to be mediated by the voltage-sensitive dye because the evoked signals had opposite polarity for 540- and 710-nm light, but no response to 850-nm light. Molecular layer stimulation of the intact cerebellum evoked slow transverse beams. Similar beams were observed in the molecular layer of thick transverse slices but not sagittal slices. With low currents, beams in transverse slices were restricted to sublayers within the molecular layer, conducting slowly away from the stimulus site. These excitatory beams were observed nearly all the way across the turtle cerebellum, distances of 4–6 mm. Microstimulation of the granule cell layer of both transverse or sagittal slices evoked a local membrane depolarization restricted to a radial wedge, but these radial responses did not activate measurable molecular layer beams in transverse slices. White matter microstimulation in sagittal slices (near the ventricular surface of the turtle cerebellum) activated the granule cell and Purkinje cell layers, but not the molecular layer. These responses were nearly synchronous, were primarily caudal to the stimulation, and were blocked by cobalt ions. Therefore, synaptic responses in all cerebellar layers contribute to optical signals recorded in intact cerebellum in vitro ( Brown and Ariel, 2009). Rapid radial signaling connects a sagittally-oriented, fast-conduction system of the deep layers with the transverse-oriented, slow-conducting molecular layer, thereby permitting complex temporal processing between two tangential but orthogonal paths in the cerebellar cortex.

Visual motion perception deficits due to cerebellar lesions are paralleled by specific changes in cerebro-cortical activity.

Recent anatomical studies have revealed strong cerebellar projections into parietal and prefrontal cortex. These findings suggest that the cerebellum might not only play a functional role in motor control but also cognitive domains, an idea also supported by neuropsychological testing of patients with cerebellar lesions that has revealed specific deficits. The goal of the present study was to test whether or not cognitive impairments after cerebellar damage are resulting from changes in cerebro-cortical signal processing. The detection of global visual motion embedded in noise, a faculty compromised after cerebellar lesions, was chosen as a model system. Using magnetoencephalography, cortical responses were recorded in a group of patients with cerebellar lesions (n = 8) and controls (n = 13) who observed visual motion of varied coherence, i.e., motion strength, presented in the peripheral visual field during controlled stationary fixation. Corroborating earlier results, the patients showed a significant impairment in global motion discrimination despite normal fixation behavior. This deficit was paralleled by qualitative differences in responses recorded from parieto-temporal cortex, including a reduced responsiveness to coherent visual motion and a striking loss of bilateral representations of motion coherence. Moreover, the perceptual thresholds correlated with the cortical representation of motion strength on single subject basis. These results demonstrate that visual motion processing in cerebral cortex critically depends on an intact cerebellum and establish a correlation between cortical activity and impaired visual perception resulting from cerebellar damage.

Recent Developments in the Understanding of Astrocyte Function in the Cerebellum In Vivo

Several studies have contributed to our understanding of astrocytes, especially Bergmann glia, in the cerebellum; but, until recently, none has looked at their function in vivo. Multicell bolus loading of fluorescent calcium indicators in combination with the astrocytic marker SR101 has allowed imaging of up to hundreds of astrocytes at once in the intact cerebellum. In addition, the selective targeting of astrocytes with fluorescent calcium indicator proteins has enabled the study of their function in vivo without the confounding effects of other neuropil signals and with a resolution that surpasses multicell bolus loading and SR101 staining. The two astrocyte types of the cerebellar cortex, Bergmann glia, and velate protoplasmic astrocytes display a diverse signaling repertoire in vivo, which ranges from localized calcium elevations in subcellular processes to waves, triggered by the release of purines and mediated by purinergic receptors that span multiple processes and can involve tens of astrocytes. During locomotor behavior, even larger numbers of astrocytes display calcium increases that are driven by neuronal activity and correlate with global changes in blood flow. In this review, we give an overview of our current understanding of the function of Bergmann glia and velate protoplasmic astrocytes and the promise of the tools used to study their calcium dynamics and function in vivo.